Japanese Patent No. 2,990,646 (JP-A 8-199070) and JP-A 2000-248166 disclose a curable composition comprising a linear perfluoropolyether compound containing at least two alkenyl groups per molecule and having a perfluoropolyether structure in its backbone, an organosilicon compound having at least two H—SiOSiO structures per molecule, and a hydrosilylation catalyst, which cures into a product having a good profile of heat resistance, chemical resistance, solvent resistance, water repellency, oil repellency and weatherability.
These perfluoropolyether rubber compositions perform well in most applications. However, their performance is short in those applications requiring chemical resistance such as sealants in semiconductor manufacturing units, sealants and potting materials for use with engine oil, and sealants and potting materials for use in engine exhaust parts. In such applications, rubber or gel products are urgently desired to prevent or retard electric or electronic parts from corrosion. In some cases, it is necessary to prevent or retard corrosion with acidic gases and sulfur-containing gases. It is thus strongly desired to have perfluoropolyether rubber or gel compositions which cure into products having oil resistance, chemical resistance, and low gas permeability and especially, minimal permeability to acidic gases and sulfur-containing gases.